Entropy measurement of a double quantum dot

Double quantum dots (DQD) offer a convenient platform for the realization and measurement of complex, experimentally tunable Hamiltonians. The electronic entropy, S, is an appealing metric to probe such Hamiltonians experimentally, as it is directly related to the degrees of freedom d of the ground state of electrons in the system, S = k_blnd. Here we present measurements of S for a system of two capacitively coupled lateral quantum dots (QD), investigating how entropy changes throughout the (0,1)↔(1,0) transition region of the stability diagram, where inter-dot Coulomb effects increase the gap to the (1,1) charge state. Although the measurements are sensitive primarily to the charge of one of the two dots, S reflects the system as a whole, which is strongly modified by coupling between the dots and to a thermal reservoir. Looked at from a different perspective, our measurement can be understood as a demonstration of the use of one QD as entropy sensor for a second quantum system, an important advance for experiments where the thermodynamics of the system of interest may be hard to probe directly.